U.S. patent application number 17/424666 was filed with the patent office on 2022-03-17 for polylactic acid resin expanded sheet, resin molded article, and method for producing polylactic acid resin expanded sheet.
This patent application is currently assigned to SEKISUI KASEI CO., LTD.. The applicant listed for this patent is SEKISUI KASEI CO., LTD.. Invention is credited to Shota ENDO, Eiji FUKUYAMA, Ayano MORI.
Application Number | 20220081554 17/424666 |
Document ID | / |
Family ID | |
Filed Date | 2022-03-17 |
United States Patent
Application |
20220081554 |
Kind Code |
A1 |
FUKUYAMA; Eiji ; et
al. |
March 17, 2022 |
POLYLACTIC ACID RESIN EXPANDED SHEET, RESIN MOLDED ARTICLE, AND
METHOD FOR PRODUCING POLYLACTIC ACID RESIN EXPANDED SHEET
Abstract
The present invention provides a polylactic acid resin expanded
sheet useful for forming a resin molded article that can easily
retain a predetermined shape. More specifically, the present
invention provides a polylactic acid resin expanded sheet including
a crystal nucleating agent and a crystallization accelerator at a
predetermined ratio, which is prepared so that a crystallization
degree becomes the predetermined state.
Inventors: |
FUKUYAMA; Eiji; (Osaka,
JP) ; ENDO; Shota; (Osaka, JP) ; MORI;
Ayano; (Osaka, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SEKISUI KASEI CO., LTD. |
Osaka |
|
JP |
|
|
Assignee: |
SEKISUI KASEI CO., LTD.
Osaka
JP
|
Appl. No.: |
17/424666 |
Filed: |
March 24, 2020 |
PCT Filed: |
March 24, 2020 |
PCT NO: |
PCT/IB2020/052724 |
371 Date: |
July 21, 2021 |
International
Class: |
C08L 67/04 20060101
C08L067/04; C08J 5/18 20060101 C08J005/18; C08K 5/14 20060101
C08K005/14; C08K 5/103 20060101 C08K005/103; C08K 3/34 20060101
C08K003/34; C08J 9/14 20060101 C08J009/14; B29C 48/00 20060101
B29C048/00; B29C 48/40 20060101 B29C048/40 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 26, 2019 |
JP |
2019-058551 |
Claims
1. A polylactic acid resin expanded sheet comprising a polylactic
acid resin, a crystal nucleating agent, and a crystallization
accelerator, wherein the expanded sheet contains 0.5 part by mass
or more and less than 3.0 parts by mass of said crystal nucleating
agent, and 0.5 part by mass or more and less than 5.0 parts by mass
of said crystallization accelerator, based on 100 parts by mass of
said polylactic acid resin, said polylactic acid resin is not
completely crystallized, a crystallization degree of said expanded
sheet is 20% or less, and said expanded sheet shows a
crystallization degree of 25% or more by being heated.
2. A resin molded article in which a part or all of the resin
molded article includes the polylactic acid resin expanded sheet
according to claim 1.
3. A method for producing a polylactic acid resin expanded sheet,
which comprises extrusion expanding a resin composition containing
a polylactic acid resin together with a blowing agent to prepare a
polylactic acid resin expanded sheet, the method further comprising
reacting polylactic acid resins together using an organic peroxide
as a radical initiator to prepare a modified polylactic acid resin,
wherein said modified polylactic acid resin has a melt tension at
190.degree. C. of 5 cN or more and 40 cN or less and is prepared
using said organic peroxide at a ratio of 0.1 part by mass or more
and 2 parts by mass or less, based on 100 parts by mass of said
polylactic acid resin, and a part or all of said polylactic acid
resin that undergoes extrusion expanding is said modified
polylactic acid resin, and said polylactic acid resin expanded
sheet is prepared using said resin composition containing 0.5 part
by mass or more and less than 3.0 parts by mass of a crystal
nucleating agent and 0.5 part by mass or more and less than 5.0
parts by mass of a crystallisation accelerator, based on 100 parts
by mass of the polylactic acid resin.
Description
TECHNICAL FIELD
[0001] The present invention relates to a polylactic acid resin
expanded sheet, a resin molded article, and a method for producing
the polylactic acid resin expanded sheet.
[0002] The present application claims the priority based on
Japanese Patent Application No. 2019-058551 filed on Mar. 26, 2019,
the contents of which are incorporated herein by reference.
BACKGROUND TECHNOLOGY
[0003] Conventionally, since a polyester resin expanded article is
lightweight, is excellent in cushioning property, and moreover, can
be easily formed and processed into a variety of shapes, it is
utilized as a raw material of various molded articles including a
packaging material and the like.
[0004] In recent years, measures against a problem that the
landscape is impaired by packaging materials that are illegally
discarded in places such as hills and fields, rivers, and coasts
are demanded.
[0005] Under such backgrounds, preparation of a molded article
using a polylactic acid resin that can be biodegraded in the
natural environment is being examined, and development of a
polylactic acid resin expanded article in various applications is
being examined.
[0006] For example, a resin molded article that has been processed
into a three-dimensional shape by thermoforming a polylactic acid
resin expanded sheet is utilized in various applications.
[0007] Meanwhile, a polylactic acid resin has
crystallizability.
[0008] A polylactic acid resin in a crystallized state exerts high
mechanical strength as compared with a polylactic acid resin in an
amorphous state.
[0009] For that reason, when a resin molded article is prepared
with the polylactic acid resin, in addition to the polylactic acid
resin usable as a base polymer, a resin composition containing a
crystal nucleating agent and a crystallization accelerator is
used.
PRIOR ART DOCUMENTS
Patent Document
[0010] Patent Document 1: Japanese Domestic Re-Publication of PCT
International Application WO 2006/121056
SUMMARY OF THE INVENTION
Problem to be Solved by the Invention
[0011] If a sheet is prepared by a producing method accompanying
rapid cooling from a thermally molten state, as is the case of a
polylactic acid resin expanded sheet, this results in that
crystallizable molecules are present in the sheet in the amorphous
state. When a resin molded article is formed with the polylactic
acid resin expanded sheet, the resin molded article is thermally
deformed, and may be unable to retain a predetermined shape.
[0012] On the other hand, if a polylactic acid resin expanded sheet
is brought into a sufficiently crystallized state, when the sheet
is subjected to thermoforming or the like, trackability to a
forming die is not sufficiently exerted, and a resin molded article
may hardly have a predetermined shape from the beginning.
[0013] That is, the conventional polylactic acid resin expanded
sheet has a problem that it is difficult to form a resin molded
article that can easily retain a predetermined shape.
[0014] Therefore, an object of the present invention is to provide
a polylactic acid resin expanded sheet useful for forming a resin
molded article that can easily retain a predetermined shape and a
method for producing the same, and consequently, a resin molded
article that can easily retain a predetermined shape.
Means for Solving the Problem
[0015] In order to solve the above-mentioned problems, the present
inventors have made intensive studies, and found out that by
containing a crystal nucleating agent and a crystallization
accelerator at a predetermined ratio, a polylactic acid resin
expanded sheet comes to have a crystallization degree, at which it
can easily show good formability in thermoforming or the like,
resulting in completion of the present invention.
[0016] That is, the present invention for solving the
above-mentioned problems provides a polylactic acid resin expanded
sheet comprising a polylactic acid resin, a crystal nucleating
agent, and a crystallization accelerator,
[0017] wherein the expanded sheet contains 0.5 part by mass or more
and less than 3.0 parts by mass of the crystal nucleating agent,
and 0.5 part by mass or more and less than 5.0 parts by mass of the
crystallization accelerator, based on 100 parts by mass of the
polylactic acid resin,
[0018] the polylactic acid resin is not completely
crystallized,
[0019] a crystallization degree of the expanded sheet is 20% or
less, and
[0020] the expanded sheet shows a crystallization degree of 25% or
more by being heated.
[0021] Also, the present invention provides a resin molded article
in which a part or all of the resin molded article includes the
polylactic acid resin expanded sheet as described above.
[0022] Further, the present invention provides a method for
producing a polylactic acid resin expanded sheet, which comprises
an extrusion step of extrusion expanding a resin composition
containing a polylactic acid resin together with a blowing agent to
prepare a polylactic acid resin expanded sheet,
[0023] the method further comprising a modification step of
reacting polylactic acid resins together using an organic peroxide
as a radical initiator to prepare a modified polylactic acid
resin,
[0024] wherein in the modification step, the modified polylactic
acid resin having a melt tension at 190.degree. C. of 5 cN or more
and 40 cN or less is prepared using the organic peroxide at a ratio
of 0.1 part by mass or more and 2 parts by mass or less, based on
100 parts by mass of the polylactic acid resin, and
[0025] in the extrusion step, a part or all of the polylactic acid
resin is the modified polylactic acid resin, and the polylactic
acid resin expanded sheet is prepared using the resin composition
containing 0.5 part by mass or more and less than 3.0 parts by mass
of a crystal nucleating agent and 0.5 part by mass or more and less
than 5.0 parts by mass of a crystallization accelerator, based on
100 parts by mass of the polylactic acid resin.
Effects of Invention
[0026] According to the present invention, there can be provided a
polylactic acid resin expanded sheet useful for forming a resin
molded article that can easily retain a predetermined shape and a
method for producing the same, as well as a resin molded article
that can easily retain a predetermined shape.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is a schematic view showing a configuration of an
apparatus for producing a polylactic acid resin expanded sheet.
BEST MODE FOR CARRYING OUT THE INVENTION
[0028] Embodiments of the present invention will be described
below.
[0029] Below, the present invention will be described using a main
example in which a polylactic acid resin expanded sheet is an
extrusion-expanded sheet that is prepared by an extrusion expansion
method.
[0030] A polylactic acid resin expanded sheet of the present
embodiment (hereinafter, also simply referred to as "expanded
sheet" or the like) is an extrusion-expanded sheet as described
above.
[0031] That is, the expanded sheet of the present embodiment is
prepared by melting and kneading a resin composition containing a
polylactic acid resin as a main component together with a blowing
agent by an extruder, and thereafter, extruding the kneaded product
into the atmospheric air through a die attached to a tip of the
extruder.
[0032] It is preferable that a polylactic acid resin of the present
embodiment is modified in order to introduce the branch structure
and the crosslinked structure, from a view point that the expanded
sheet is brought into the good expanded state.
[0033] That is, it is preferable that a part or all of the
polylactic acid resin contained in the above-mentioned resin
composition to be supplied to extrusion expansion is a modified
polylactic acid resin (hereinafter, also referred to as "modified
polylactic acid resin").
[0034] In the present embodiment, a polylactic acid resin before
modification (hereinafter, also referred to as "unmodified
polylactic acid resin"), which is a raw material of the
above-mentioned modified polylactic acid resin, may be a
homopolymer of lactic acid, or may be a copolymer of lactic acid
and other monomer.
[0035] Examples of other monomer in the above-mentioned copolymer
include aliphatic hydroxycarboxylic acids other than lactic acid,
aliphatic polyhydric alcohols, aliphatic polycarboxylic acids, and
the like.
[0036] The above-mentioned another monomer may be, for example,
polyfunctional polysaccharides or the like.
[0037] Lactic acid constituting the above-mentioned unmodified
polylactic acid resin may be any one of an L-isomer and a D-isomer,
or both of them.
[0038] That is, the above-mentioned unmodified polylactic acid
resin that is the above-mentioned homopolymer may be any of a
poly(L-lactic acid) resin, a poly(D-lactic acid) resin, and a
poly(DL-lactic acid) resin.
[0039] Examples of the aliphatic polycarboxylic acid constituting
the above-mentioned copolymer include, for example, oxalic acid,
succinic acid, malonic acid, glutaric acid, adipic acid, pimelic
acid, suberic acid, azelaic acid, undecanedioic acid, dodecanedioic
acid, and the like.
[0040] The aliphatic polycarboxylic acid may be an andydride.
[0041] Examples of the above-mentioned aliphatic polyhydric alcohol
include, for example, ethylene glycol, diethylene glycol,
triethylene glycol, propylene glycol, dipropylene glycol,
1,3-butanediol, 1,4-butanediol, 3-methyl-1,5-pentanediol,
1,6-hexanediol, 1,9-nonanediol, neopentyl glycol, tetramethylene
glycol, 1,4-cyclohexanedimethanol, and the like.
[0042] Examples of the aliphatic hydroxycarboxylic acid other than
lactic acid, which constitutes the above-mentioned copolymer,
include, for example, glycolic acid, 3-hydroxybutyric acid,
4-hydroxybutyric acid, 4-hydroxyvaleric acid, 5-hydroxyvaleric
acid, 6-hydroxycaproic acid, and the like.
[0043] Examples of the above-mentioned polyfunctional
polysaccharides include, for example, cellulose, cellulose nitrate,
methylcellulose, ethylcellulose, celluloid, viscose rayon,
regenerated cellulose, cellophane, cupra, cuprammonium rayon,
cuprophane, Bemberg, hemicellulose, starch, acropectin, dextrin,
dextran, glycogen, pectin, chitin, chitosan, arabic gum, guar gum,
locust bean gum, acacia gum, and the like.
[0044] The above-mentioned unmodified polylactic acid resin in the
present embodiment is preferably such that a structural part
derived from lactic acid (L-isomer and D-isomer) is contained in a
molecule at a ratio of 50% by mass or more.
[0045] The content of the above-mentioned structural part (L-isomer
and D-isomer) is more preferably 60% by mass or more, further
preferably 70% by mass or more, particularly preferably 80% by mass
or more.
[0046] The above-mentioned unmodified polylactic acid resin can be
made into a modified polylactic acid resin by reacting the
above-mentioned polylactic acid resins together using a radical
initiator such as an organic peroxide.
[0047] It is preferable that the above-mentioned modified
polylactic acid resin of the present embodiment is prepared so as
to show specific characteristic values in measurement of the melt
tension at 190.degree. C. and measurement of the elongational
viscosity at the same temperature.
[0048] Specifically, the modified polylactic acid resin shows the
melt tension of 5 cN or more and 40 cN or less in measurement of
the melt tension at 190.degree. C.
[0049] The above-mentioned melt tension of the modified polylactic
acid resin is preferably 39 cN or less, more preferably 37 cN or
less, particularly preferably 35 cN or less.
[0050] The above-mentioned melt tension of the modified polylactic
acid resin is preferably 8 cN or more, more preferably 10 cN or
more.
[0051] The modified polylactic acid resin of the present embodiment
can suppress foam breakage when an expanded sheet is prepared by
extrusion expansion using the above-mentioned resin composition, by
the melt tension being 5 cN or more.
[0052] The modified polylactic acid resin of the present embodiment
can suppress foam breakage by good elongation of a foam film shown
at expansion, by the melt tension being 40 cN or less.
[0053] The melt tension of the modified polylactic acid resin or
the unmodified polylactic acid resin at 190.degree. C. can be
measured using a twin-bore type capillary rheometer "Rheologic
5000T" (manufactured by CEAST) as follows:
(Method of Measuring Melt Tension)
[0054] Each sample is vacuum-dried at 80.degree. C. for 5 hours,
thereafter, sealed, and stored in a desiccator until immediately
before measurement.
[0055] A measurement sample resin is filled into a barrel having a
diameter of 15 mm, which has been heated at a test temperature of
190.degree. C., and is pre-heated for 5 minutes. Thereafter, the
pre-heated sample is extruded into a string form from a capillary
die (caliber 2.095 mm, length 8 mm, inflow angle 90 degree
(conical)) of the above-mentioned measuring device while a piston
descending speed (0.07730 mm/s) is retained constant, this
string-form product is passed through a tension detection pulley
positioned 27 cm below the above-mentioned capillary die, and
thereafter, is wound using a wind-up roll while a winding speed
thereof is gradually increased at an initial speed of 4.0 mm/s and
acceleration of 12 mm/s.sup.2. An average of a maximum value and a
minimum value immediately before breakage of the string-form
product is employed as a melt tension of the sample.
[0056] In addition, when the number of maximum points on a tension
chart is only one, its maximum value is employed as the melt
tension.
[0057] It is preferable that the modified polylactic acid resin
shows suitable flowability at thermal melting, and it is preferable
that a melt mass flow rate (MFR) is 0.5 g/10 min or more.
[0058] MFR of the modified polylactic acid resin is more preferably
1.0 g/10 min or more, further preferably 1.5 g/10 min or more,
particularly preferably 2.0 g/10 min or more.
[0059] The above-mentioned MFR is preferably 20 g/10 min or less,
more preferably 10 g/10 min or less, particularly preferably 6.0
g/10 min or less.
[0060] A melt mass flow rate (MFR) of the modified polylactic acid
resin or the unmodified polylactic acid resin can be measured
using, for example, "Melt Flow Index Tester (automatic) 120-SAS"
manufactured by YASUDA SEIKI SEISAKUSHO, LTD.
[0061] MFR is measured in accordance with b) a method of measuring
the time for which the piston moves a predetermined distance
described in the method B of JIS K7210-1: 2014
"Plastics--Determination of the melt mass-flow rate (MFR) and melt
volume-flow rate (MVR) of thermoplastics--Part 1".
[0062] The measuring conditions are as follows: [0063] Sample: 3 to
8 g
[0064] In addition, a sample for measurement is vacuum-dried at
80.degree. C. for 5 hours, and after drying, sealed and stored in a
desiccator until immediately before measurement. [0065]
Pre-heating: 300 seconds [0066] Load hold: 30 seconds [0067] Test
temperature: 190.degree. C. [0068] Test load: 2.16 kg (21.18 N)
[0069] The sample is tested three times, and an average thereof is
employed as a value of a melt mass flow rate (g/10 min).
[0070] When the above-mentioned unmodified polylactic acid resin is
modified, not only a radical initiator but also a chain extender
such as carbodiimide may be used.
[0071] Modification with the chain extender can be performed using
a compound having one or a plurality of functional groups that can
condense with a hydroxy group or a carboxyl group present in the
molecular structure of the polylactic acid resin, such as an
acrylic-based organic compound, an epoxy-based organic compound,
and an isocyanate-based organic compound.
[0072] That is, the above-mentioned modification can be carried out
by a method of binding an acrylic-based organic compound, an
epoxy-based organic compound, an isocyanate-based organic compound
or the like to a polylactic acid resin by a reaction.
[0073] Modification of the polylactic acid resin by crosslinking or
long chain branching can be performed by a method of reacting
polylactic acid resins together by the radical initiator or the
like, as described above.
[0074] Among the above-mentioned modification methods, it is
preferable to react polylactic acid resins together by the radical
initiator, in that other components can be inhibited from being
contained in the expanded sheet.
[0075] In addition, when polylactic acid resins are reacted
together using the radical initiator having the suitable
reactivity, a degradation starting point of the polylactic acid
resin in the extruder is attacked by a free radical generated by
the above-mentioned radical initiator, the position becomes a
crosslinked point (branching point), and the resin is
stabilized.
[0076] In the polylactic acid resin, the thermal stability is
increased by such modification, and reduction in a molecular weight
becomes difficult when the resin passes through the extruder.
[0077] Examples of the above-mentioned radical initiator used in
modification of the polylactic acid resin include, for example,
organic peroxides, azo compounds, halogen molecules, and the
like.
[0078] Among them, an organic peroxide is preferable.
[0079] Examples of the organic peroxide used in the present
embodiment include, for example, peroxyester, hydroperoxide,
dialkyl peroxide, diacyl peroxide, peroxydicarbonate, peroxyketal,
ketone peroxide, and the like.
[0080] Examples of the above-mentioned peroxyester include, for
example, t-butylperoxy 2-ethylhexyl carbonate, t-hexylperoxy
isopropyl monocarbonate, t-hexyl peroxybenzoate, t-butyl
peroxybenzoate, t-butyl peroxylaurate, t-butyl
peroxy-3,5,5-trimethylhexanoate, t-butyl peroxyacetate,
2,5-dimethyl-2,5-di(benzoylperoxy)hexane, t-butyl peroxyisopropyl
monocarbonate, and the like.
[0081] Examples of the above-mentioned hydroperoxide include, for
example, permethane hydroperoxide, diisopropylbenzene
hydroperoxide, cumene hydroperoxide, t-butyl hydroperoxide, and the
like.
[0082] Examples of the above-mentioned dialkyl peroxide include,
for example, dicumyl peroxide, di-t-butyl peroxide,
2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3, and the like.
[0083] Examples of the above-mentioned diacyl peroxide include, for
example, dibenzoyl peroxide, di(4-methylbenzoyl) peroxide,
di(3-methylbenzoyl) peroxide, and the like.
[0084] Examples of the above-mentioned peroxydicarbonate include,
for example, di(2-ethylhexyl) peroxydicarbonate, diisopropyl
peroxydicarbonate, and the like.
[0085] Examples of the above-mentioned peroxyketal include, for
example, 1,1-di-t-butylperoxy-3,3,5-trimethylcyclohexane,
1,1-di-t-butylperoxycyclohexane, 2,2-di(t-butylperoxy)butane,
n-butyl 4,4-di-(t-butylperoxy)valerate,
2,2-bis(4,4-di-t-butylperoxycyclohexyl)propane, and the like.
[0086] Examples of the above-mentioned ketone peroxide include, for
example, methyl ethyl ketone peroxide, acetylacetone peroxide, and
the like.
[0087] In modification with the above-mentioned organic peroxide,
there is a possibility that a component having an excessively large
molecular weight, which becomes the gel at thermal melting, is
mixed into the modified polylactic acid resin after modification,
and a problem of the odor due to the decomposition residue of the
organic peroxide is generated.
[0088] The above-mentioned organic peroxide is preferably a
peroxyester, in that such a problem can be inhibited from being
generated, and the polylactic acid resin can be easily modified
into the state suitable for expansion.
[0089] Among peroxyesters, the organic peroxide used in
modification of the polylactic acid resin is preferably a
peroxycarbonate-based organic peroxide such as peroxymonocarbonate
and peroxydicarbonate.
[0090] Among peroxycarbonate-based organic peroxides, the organic
peroxide used in modification of the polylactic acid resin in the
present embodiment is preferably a peroxymonocarbonate-based
organic peroxide, particularly preferably t-butylperoxyisopropyl
monocarbonate.
[0091] The organic peroxide as described above is usually used at
the content of 0.1 part by mass or more based on 100 parts by mass
of the unmodified polylactic acid resin to be modified, depending
on a molecular weight thereof or the like.
[0092] The content of the above-mentioned organic peroxide is
preferably 0.2 part by mass or more, particularly preferably 0.3
part by mass or more.
[0093] The content of the organic peroxide is preferably 2.0 parts
by mass or less, more preferably 1.5 parts by mass or less,
particularly preferably 1.0 part by mass or less.
[0094] By modifying the unmodified polylactic acid resin using the
organic peroxide at such a content, the modified polylactic acid
resin after modification can be made suitable for expansion.
[0095] The organic peroxide as described above can more reliably
exert the effect due to modification on the polylactic acid resin,
by using the content thereof of 0.1 part by mass or more.
[0096] On the other hand, the organic peroxide can inhibit
interminglement of the gel in the polylactic acid resin after
modification, by using the content thereof of 2.0 parts by mass or
less.
[0097] The polylactic acid resin in the resin composition to be
supplied to extrusion expansion may also be a mixture of the
modified polylactic acid resin and the unmodified polylactic acid
resin.
[0098] A ratio of the modified polylactic acid resin occupied in a
total amount of the polylactic acid resin in the above-mentioned
resin composition is preferably 60% by mass or more, more
preferably 70% by mass or more, further preferably 80% by mass or
more, particularly preferably 90% by mass or more.
[0099] A resin other than the polylactic acid resin may be
contained in the above-mentioned resin composition as necessary,
and the content of the resin other than the polylactic acid resin
is preferably 10% by mass or less, more preferably 5% by mass or
less, further preferably 3% by mass or less.
[0100] It is preferable that the resin composition to be supplied
to extrusion expansion contains a crystal nucleating agent and a
crystallization accelerator, together with the above-mentioned
polylactic acid resin.
[0101] Examples of the above-mentioned crystal nucleating agent
include, for example, an organic crystal nucleating agent, an
inorganic crystal nucleating agent, and the like.
[0102] As the above-mentioned crystal nucleating agent, only one of
the organic crystal nucleating agent and the inorganic crystal
nucleating agent may be employed, or the organic crystal nucleating
agent and the inorganic crystal nucleating agent may be used
together.
[0103] When only the inorganic crystal nucleating agent is used as
the above-mentioned crystal nucleating agent, only one kind of
inorganic crystal nucleating agents listed later may be employed,
or two or more kinds may be used together.
[0104] Similarly, when only the organic crystal nucleating agent is
used as the above-mentioned crystal nucleating agent, only one kind
of organic crystal nucleating agents listed later may be employed,
or two or more kinds may be used together.
[0105] As the above-mentioned crystal nucleating agent, when the
organic crystal nucleating agent and the inorganic crystal
nucleating agent are used together, a plurality of kinds may be
employed in any one of or both of the organic crystal nucleating
agent and the inorganic crystal nucleating agent.
[0106] Examples of the above-mentioned inorganic crystal nucleating
agent include, for example, talc, tin oxide, smectite, bentonite,
dolomite, sericite, feldspar powder, kaolin, mica, montmorillonite,
and the like.
[0107] From a view point of improvement in a crystallization rate,
the heat resistance, the durability, and the like, it is preferable
that, among these, the above-mentioned inorganic crystal nucleating
agent is talc or tin oxide.
[0108] Examples of the above-mentioned organic crystal nucleating
agent include, for example, organic amide compounds, organic
hydrazide compounds, carboxylic acid ester-based compounds, organic
sulfonic acid salts, phthalocyanine-based compounds, melamine-based
compounds, organic phosphonic acid salts, and the like.
[0109] As the organic sulfonic acid salt, various organic sulfonic
acid salts such as a sulfoisophthalic acid salt can be used, and
among them, a dimethyl 5-sulfoisophthalate metal salt is
preferable, from a view point of the crystallization promoting
effect.
[0110] Further, a barium salt, a calcium salt, a strontium salt, a
potassium salt, a rubidium salt, a sodium salt, and the like are
preferable.
[0111] Examples of the above-mentioned organic amide compound
include, for example, N,N',N''-tricyclohexyltrimesic acid amide,
N,N'-ethylenebis(12-hydroxystearic acid) amide, and the like.
[0112] The content of the above-mentioned crystal nucleating agent
in the above-mentioned resin composition can be, for example, 0.5
part by mass or more, when the content of the above-mentioned
polylactic acid resin contained in the above-mentioned resin
composition is 100 parts by mass.
[0113] The content of the above-mentioned crystal nucleating agent
in the above-mentioned resin composition is preferably 0.6 part by
mass or more, more preferably 0.7 part by mass or more.
[0114] The content of the above-mentioned crystal nucleating agent
in the above-mentioned resin composition can be, for example, less
than 3.0 parts by mass, when the content of the above-mentioned
polylactic acid resin contained in the above-mentioned resin
composition is 100 parts by mass.
[0115] The content of the above-mentioned crystal nucleating agent
in the above-mentioned resin composition is preferably 2.5 parts by
mass or less, more preferably 2.2 parts by mass or less.
[0116] Examples of the above-mentioned crystallization accelerator
include, for example, phthalic acid derivatives such as di-n-octyl
phthalate, di-2-ethylhexyl phthalate, dibenzyl phthalate,
diisodecyl phthalate, ditridecyl phthalate, and diundecyl
phthalate, isophthalic acid derivatives such as dioctyl
isophthalate, adipic acid derivatives such as di-n-butyl adipate
and dioctyl adipate, maleic acid derivatives such as di-n-butyl
maleate, citric acid derivatives such as tri-n-butyl citrate,
itaconic acid derivatives such as monobutyl itaconate, oleic acid
derivatives such as butyl oleate, ricinoleic acid derivatives such
as glycerin monoricinoleate, phosphoric acid esters such as
tricresyl phosphate and trixylenyl phosphate, hydroxy
polycarboxylic acid esters such as polyethylene adipate and
tributyl polyacrylate acetylcitrate, polyhydric alcohol esters such
as glycerin triacetate and glycerin tripropionate, polyalkylene
glycol derivatives such as polyethylene glycol and polypropylene
glycol, benzyl 2-(2-methoxyethoxy)ethyl adipate, polyglycerin fatty
acid ester, and the like.
[0117] As the above-mentioned crystallization accelerator,
polyglycerin fatty acid ester is preferable.
[0118] Examples of the above-mentioned polyglycerin fatty acid
esters include, for example, polyglycerin oleic acid ester,
polyglycerin ricinoleic acid ester, polyglycerin lauric acid ester,
polyglycerin stearic acid ester, polyglycerin condensed ricinoleic
acid ester, and the like.
[0119] As the above-mentioned crystallization accelerator, among
these, it is preferable to employ polyglycerin stearic acid
ester.
[0120] The polyglycerin fatty acid ester is generally utilized as a
plasticizer, and can be one that inhibits crystallization to the
polylactic acid resin.
[0121] However, the polyglycerin fatty acid ester has a function of
promoting formation of a crystal nucleus by the polylactic acid
resin, and has a function of promoting formation of the crystal
nucleus to promote crystallization.
[0122] In the present embodiment, as the polylactic acid resin, the
modified polylactic acid resin is employed.
[0123] That is, since the polylactic acid resin in the present
embodiment has the molecular structure such as branching and
crosslinking, crystals hardly grow large.
[0124] Accordingly, it can be said that the polyglycerin fatty acid
ester that does not promote crystal growth, but exerts the function
of promoting formation of the crystal nucleus is suitable as the
crystallization accelerator used in the present embodiment.
[0125] The content of the above-mentioned crystallization
accelerator in the above-mentioned resin composition can be, for
example, 0.5 part by mass or more, when the content of the
above-mentioned polylactic acid resin contained in the
above-mentioned resin composition is 100 parts by mass.
[0126] The content of the above-mentioned crystallization
accelerator in the above-mentioned resin composition is preferably
0.6 part by mass or more, more preferably 0.7 part by mass or
more.
[0127] The content of the above-mentioned crystallization
accelerator in the above-mentioned resin composition can be, for
example, less than 5.0 parts by mass, when the content of the
above-mentioned polylactic acid resin contained in the
above-mentioned resin composition is 100 parts by mass.
[0128] The content of the above-mentioned crystallization
accelerator in the above-mentioned resin composition is preferably
4.0 parts by mass or less, more preferably 3.5 parts by mass or
less.
[0129] Various additives can be added to the above-mentioned resin
composition as necessary.
[0130] Examples of the additive include, for example, cell
adjusting agents, lubricants, antioxidants, antistatic agents,
flame retardants, ultraviolet absorbing agents, light stabilizers,
coloring agents, antibacterial agents, and the like.
[0131] In addition, the content of the above-mentioned additive is
preferably 10 parts by mass or less, more preferably 5 parts by
mass or less, based on 100 parts by mass of the polylactic acid
resin.
[0132] As the above-mentioned blowing agent that is used in
extrusion expansion together with the above-mentioned resin
composition, a physical blowing agent that becomes the gas at an
ambient temperature (23.degree. C.) and an ambient pressure (1
atm), or a decomposable blowing agent that generates the gas by
thermal decomposition can be employed.
[0133] As the above-mentioned physical blowing agent, for example,
an inert gas, an aliphatic hydrocarbon, an alicyclic hydrocarbon,
and the like can be employed.
[0134] Examples of the above-mentioned inert gas include, for
example, carbon dioxide, nitrogen, and the like.
[0135] Examples of the above-mentioned aliphatic hydrocarbon
include, for example, propane, normal butane, isobutane, normal
pentane, isopentane, and the like, and examples of the
above-mentioned alicyclic hydrocarbon include, for example,
cyclopentane, cyclohexane, and the like.
[0136] In the present embodiment, among the above-mentioned
examples, particularly, normal butane and isobutane can be
preferably used.
[0137] Examples of the above-mentioned decomposable blowing agent
include azodicarbonamide, dinitrosopentamethylenetetramine, sodium
bicarbonate, or a mixture of an organic acid such as citric acid or
a salt thereof and a bicarbonate salt, and the like.
[0138] When the trackability to the die surface at the time of
formation is taken into consideration, it is preferable that the
expanded sheet of the present embodiment, which is prepared using
the resin composition as described above, is in the state where it
exerts softness to a certain degree.
[0139] An open cell ratio of the expanded sheet of the present
embodiment is preferably 10% or more, more preferably 15% or
more.
[0140] In order to make the expanded sheet exert the excellent
strength, an open cell ratio of the expanded sheet is preferably
50% or less, more preferably 40% or less, particularly preferably
30% or less.
[0141] An expansion ratio of the expanded sheet is preferably 3
times or more, more preferably 4 times or more, particularly
preferably 4.5 times or more.
[0142] In order to exert the excellent strength, the expansion
ratio of the expanded sheet is preferably 15 times or less, more
preferably 12 times or less, particularly preferably 10 times or
less.
[0143] An open cell ratio of the expanded sheet is measured by a
method shown below.
(Open Cell Ratio)
[0144] A plurality of 25 mm length and 25 mm width sheet-like
samples are excised from the expanded sheet, the excised samples
are overlapped so as not to form gaps, to obtain a measurement
sample having a thickness of 25 mm, the external dimension of this
measurement sample is measured to 1/100 mm using "DIGIMATIC
CALIPER" manufactured by Mitutoyo Corporation, and the apparent
volume (cm.sup.3) is obtained.
[0145] Then, the volume (cm.sup.3) of the measurement sample is
obtained by the 1-1/2-1 atm method using Air Comparison Pycnometer
type 1000 (manufactured by Tokyo Science Co., Ltd.).
[0146] By these obtained values and the equation below, an open
cell ratio (%) is calculated, and an average of the number of tests
(5 times) is obtained.
[0147] In addition, the measurement sample is conditioned for 16
hours under the standard atmosphere of JIS K7100-1999, symbol
"23/50" (temperature 23.degree. C., relative humidity 50%), class
2, and thereafter, measurement is performed under the same standard
atmosphere.
[0148] Besides, the air comparison pycnometer is corrected with a
standard sphere (large 28.9 cc, small 8.5 cc).
Open cell ratio (%)=100.times.(apparent volume-volume measured with
air comparison pycnometer)/apparent volume
[0149] An expansion ratio of the expanded sheet can be obtained by
obtaining the apparent density (.rho.1) of the expanded sheet,
obtaining the density (true density: .rho.0) of the polylactic acid
resin composition constituting the expanded sheet, and dividing the
true density (.rho.0) by the above-mentioned apparent density
(.rho.1).
[0150] That is, an expansion ratio is obtained by calculation by
the equation below.
Expansion ratio=true density (.rho.0)/apparent density (.rho.1)
[0151] The density of the above-mentioned expanded sheet can be
obtained by a method described in JIS K7222: 1999 "Cellular
plastics and rubbers--Determination of apparent density", and is
specifically measured by a method described below.
(Density Measurement Method)
[0152] A sample of 100 cm.sup.3 or more is cut from the expanded
sheet so as not to change the original cell structure, this sample
is conditioned for 16 hours under the standard atmosphere of JIS
K7100: 1999, symbol "23/50" (temperature 23.degree. C., relative
humidity 50%), class 2, thereafter, the dimension and the mass
thereof are measured, and the density is calculated by the
following equation:
Apparent density (kg/m.sup.3)=mass of sample (kg)/volume of sample
(m.sup.3)
[0153] In addition, for measuring the dimension of the sample, for
example, "DIGIMATIC" type CD-15 manufactured by Mitutoyo
Corporation can be used.
[0154] The density of the polylactic acid resin composition can be
obtained by performing measurement based on the Archimedes method
(the in-liquid weighing method in JIS K8807: 2012 "Methods of
measuring density and specific gravity of solid"), on a sample that
has been converted into a non-expanded article by thermal pressing
of the expanded sheet or the like.
[0155] Since it is preferable that the above-mentioned expanded
sheet shows the good formability when a resin molded article is
formed, and exerts the excellent strength to the resin molded
article after formation, it is preferable that the above-mentioned
polylactic acid resin constituting a foam film has not been
completely crystallized, and for example, is in the state where
crystallization progresses by heating to a glass transition
initiation temperature or higher.
[0156] It is preferable that the above-mentioned expanded sheet has
a crystallization degree of 20% or less, in that a desired shape
can be easily imparted by thermoforming or the like.
[0157] A crystallization degree of the above-mentioned expanded
sheet is more preferably 19% or less, further preferably 18% or
less.
[0158] In order to make a resin molded article exert the excellent
strength, it is preferable that the above-mentioned expanded sheet
is brought into the state where it shows a crystallization degree
of 25% or more by being heated.
[0159] In order to make a resin molded article exert the excellent
strength, it is more preferable that the above-mentioned expanded
sheet is brought into the state where it shows a crystallization
degree of 30% or more, and it is further preferable that the
expanded sheet is brought into the state where it shows a
crystallization degree of 35% or more, by being heated.
[0160] If a crystallization degree of the above-mentioned expanded
sheet is excessively low, or a crystallization degree that is
reached by heating of the above-mentioned expanded sheet is
excessively high, change in a crystallization degree upon
preparation of a resin molded article may become large, or a resin
molded article may be brought into the state where it has not been
sufficiently crystallized.
[0161] From the above, a crystallization degree of the
above-mentioned expanded sheet is preferably 8% or more, more
preferably 10% or more, further preferably 12% or more,
particularly preferably 14% or more.
[0162] It is preferable that a crystallization degree that is
reached by heating of the above-mentioned expanded sheet is 50% or
less.
[0163] A crystallization degree of the above-mentioned expanded
sheet is more preferably 45% or less, further preferably 40% or
less, particularly preferably 38% or less.
[0164] A crystallization degree of each of the polylactic acid
resin, the expanded sheet, and the resin molded article or the like
is obtained as follows:
(Crystallization Degree)
[0165] A crystallization degree of each of the polylactic acid
resin, the expanded sheet, and the resin molded article is measured
using a heat flux differential scanning calorimeter (heat flux DSC)
as follows:
[0166] Measurement is performed by a method described in JIS K7122:
1987, JIS K7122: 2012 "Testing methods for heat of transitions of
plastics".
[0167] Provided that a sampling method/temperature conditions are
performed as follows:
[0168] 5.+-.0.5 mg of a sample is filled on a bottom of a
measurement container made of aluminum (manufactured by Hitachi
High-Tech Science Corporation, product code: GAA-0065) so as not to
form gaps, and thereafter, the container is closed with an aluminum
lid (manufactured by Hitachi High-Tech Science Corporation, product
code: GAA-0064). Then, using a differential scanning calorimeter
("DSC7000X, AS-3" manufactured by Hitachi High-Tech Science
Corporation), the closed container is retained at 30.degree. C. for
2 minutes under a nitrogen gas flow rate of 20 mL/min, and a DSC
curve when a temperature is raised from 30.degree. C. to
210.degree. C. at a speed of 2.degree. C./min is obtained.
[0169] As a standard substance at that time, alumina is used.
[0170] Herein, "crystallization degree" is a value obtained by
dividing a difference between a heat absorption amount (melting
heat amount (J/g)) obtained from an area of an endothermic peak
appearing in crystal melting and a crystallization heat amount
(J/g) obtained from an area of a crystallization peak, by the
theoretical melting heat of a polylactic acid perfect crystal (93
J/g).
[0171] A melting heat amount and a crystallization heat amount are
calculated using an analytical software attached to a device.
[0172] Specifically, a melting heat amount is calculated from a
part surrounded by a straight line binding a point at which a DSC
curve leaves from a low temperature side base line and a point at
which the DSC curve returns again to a high temperature side base
line, and the DSC curve.
[0173] A crystallization heat amount is calculated from an area of
a part surrounded by a straight line binding a point at which a DSC
curve leaves from a low temperature side base line and a point at
which the DSC curve returns again to a high temperature side, and
the DSC curve.
[0174] That is, a crystallization degree is obtained from the
following equation:
Crystallization degree (%)=[Melting heat amount
(J/g)-crystallization heat amount (J/g)]/93 (J/g).times.100
[0175] A crystallization degree that can be reached by heating of
the above-mentioned expanded sheet is obtained by dividing the
above-mentioned melting heat amount (J/g) by the theoretical
melting heat of a polylactic acid perfect crystal (93 J/g).
Crystallization degree that can be reached by expanded sheet
(%)=melting heat amount (J/g)/93 (J/g).times.100
[0176] A crystallization degree of the above-mentioned expanded
sheet can be adjusted by use amounts of the above-mentioned crystal
nucleating agent and the above-mentioned crystallization
accelerator, conditions in extrusion expansion (resin temperature
and cooling conditions immediately after extrusion), and the
like.
[0177] One example of a method for producing an expanded sheet
according to the present embodiment will be described below.
[0178] A method for producing a polylactic acid resin expanded
sheet according to the present embodiment includes an extrusion
step of extrusion expanding a resin composition containing a
polylactic acid resin together with a blowing agent to prepare a
polylactic acid resin expanded sheet.
[0179] As described above, in the present embodiment, the method
further includes a modification step of reacting polylactic acid
resins together using an organic peroxide as a radical initiator to
prepare a modified polylactic acid resin.
[0180] In the above-mentioned modification step, the
above-mentioned modified polylactic acid resin having a melt
tension at 190.degree. C. of 5 cN or more and 40 cN or less is
prepared using the above-mentioned organic peroxide at a ratio of
0.1 part by mass or more and 2 parts by mass or less, based on 100
parts by mass of the above-mentioned polylactic acid resin.
[0181] In the above-mentioned extrusion step, a part or all of the
above-mentioned polylactic acid resin is the above-mentioned
modified polylactic acid resin, and the above-mentioned polylactic
acid resin expanded sheet is prepared using 0.5 part by mass or
more and less than 3.0 parts by mass of the above-mentioned crystal
nucleating agent and 0.5 part by mass or more and less than 5.0
parts by mass of the above-mentioned crystallization accelerator,
based on 100 parts by mass of the polylactic acid resin.
[0182] The above-mentioned modification step can be performed by
melting and kneading an unmodified polylactic acid resin and an
organic peroxide with a kneader or a twin screw extruder, or the
like.
[0183] In this step, the unmodified polylactic acid resin is heated
and melted, and at the same time, the organic peroxide is thermally
decomposed to generate a radical, and cutting and crosslinking
reactions are caused in a molecule of the polylactic acid resin by
the radical, and by performing melting and kneading for a
predetermined time, a modified polylactic acid resin with the
branch structure and the crosslinked structure formed therein is
obtained.
[0184] In the above-mentioned modification step, for example, the
modified polylactic acid resin may be pelletized immediately
thereafter, using a twin screw extruder installed with a
granulation die (hot cut die).
[0185] A strand die or a T die is installed in the twin screw
extruder used in the above-mentioned modification step, and in the
above-mentioned modification step, a strand or a sheet of the
modified polylactic acid resin is prepared, and thereafter, a step
of cutting the strand or the sheet to perform granulation may be
performed separately.
[0186] In addition, if necessary, the extrusion expansion step may
be performed using a tandem extruder, subsequently to the
modification step.
[0187] In addition, if necessary, the extrusion expansion step may
be performed using a tandem extruder, subsequently to the
modification step.
[0188] For example, the extrusion expansion step in the present
embodiment can be performed using an apparatus as shown in FIG.
1.
[0189] An apparatus exemplified in FIG. 1 includes a tandem
extruder 10, and a circular die CD for discharging a polylactic
acid resin composition that has been melted and kneaded in the
tandem extruder 10, into a cylindrical form.
[0190] Further, this producing apparatus includes a cooling device
CL for air-cooling an expanded sheet that has been discharged from
the circular die CD into a cylindrical form, a mandrel MD for
enlarging a diameter of this cylindrical expanded sheet to a
cylinder having the predetermined size, a slit device for slitting
the expanded sheet after its passage through the mandrel MD to
divide it into two sheets, and a wind-up roller 22 for winding the
slitted expanded sheet 1 after its passage through a plurality of
rollers 21.
[0191] In an upstream extruder (hereinafter, also referred to as
"first extruder 10a") of the above-mentioned tandem extruder 10, a
hopper 11 for charging a polylactic acid resin that is a raw
material of an expanded sheet, and a gas introduction part 12 for
supplying a blowing agent such as a hydrocarbon into a cylinder are
provided.
[0192] On a downstream side of this first extruder 10a, an extruder
(hereinafter, also referred to as "second extruder 10b") for
melting and kneading a polylactic acid resin composition containing
a blowing agent is arranged.
[0193] When an extrusion expansion step is performed with such an
apparatus, it is also possible to perform modification of a
polylactic acid resin with the first extruder 10a, mix a blowing
agent and the like at a terminal end part of the first extruder 10a
or a basic end part of the second extruder 10b to prepare a
polylactic acid resin composition that is a raw material of an
expanded sheet, and perform extrusion expansion from the
above-mentioned circular die CD.
[0194] The expanded sheet of the present embodiment can be
prevented from being completely crystallized until a state where a
polylactic acid resin contained in the expanded sheet cannot be
crystallized any more, by strengthening cooling with a cooling
device CL.
[0195] That is, the expanded sheet can be prepared in the state
where a crystallization degree is suppressed low, by strengthening
cooling with the cooling device CL.
[0196] In addition, the expanded sheet of the present embodiment
can be prepared in the state where a crystallization degree is
suppressed low, by shortening the time until the expanded sheet
reaches the mandrel MD, after being extruded from the circular die
CD.
[0197] The expanded sheet that has been prepared in the state where
a crystallization degree is 20% or less, in this way, can be easily
deformed by heating, and moreover, a crystal nucleating agent and a
crystallization accelerator are contained at an appropriate ratio,
and accordingly, occurrence of rapid crystallization is suppressed
upon forming.
[0198] Further, in the present embodiment, since a polylactic acid
resin contained in the expanded sheet is a modified polylactic acid
resin, occurrence of rapid crystallization is suppressed upon
forming.
[0199] Accordingly, the expanded sheet prepared in the present
embodiment shows good trackability to the die surface of a forming
die, and after forming, crystallization progresses adequately, and
thermal deformation thereafter can be hardly caused.
[0200] A resin molded article of the present embodiment can be
produced by processing an expanded sheet by a method called
thermoforming or the like.
[0201] Examples of the above-mentioned thermoforming include,
vacuum forming, pressure forming, vacuum/pressure forming, matched
molding forming, press forming, and the like.
[0202] The above-mentioned vacuum forming may be an air slip method
or a plug assist method.
[0203] In the resin molded article, it is preferable that a
polylactic acid resin contained therein is sufficiently
crystallized, by being heated at this forming, or by being heated
in the state where a shape thereof is retained, after forming.
[0204] Specifically, the resin molded article is prepared so that a
crystallization degree becomes preferably 80% or more, more
preferably 90% or more relative to a finally reachable
crystallization degree.
[0205] The method for producing the resin molded article is not
particularly limited to the method as described above.
[0206] In addition, it is not necessary to form the resin molded
article using only the expanded sheet of the present embodiment,
and the resin molded article may be formed further using a member
other than the expanded sheet.
[0207] For example, the resin molded article may be such that a
resin film or a piece of paper is bonded to an outer peripheral
surface of a cup container or a bowl container that have been
formed with the expanded sheet of the present embodiment.
[0208] The expanded sheet constituting a part or all of the
above-mentioned resin molded article does not necessarily have a
three-dimensional shape.
[0209] For example, the resin molded article may be formed only of
a plate-like expanded sheet like a thin wooden box.
[0210] The resin molded article in the present embodiment can more
remarkably exert the effect of the present invention, by being a
resin molded article like a thin wooden box, which easily becomes
visually conspicuous only by generation of a slight strain.
[0211] That is, it is preferable that the resin molded article in
the present embodiment contains a plate-like expanded sheet as a
constituent member.
[0212] In addition, the present invention is not at all limited to
the previously stated exemplifications, and the above-mentioned
exemplifications can be appropriately modified.
Example S
[0213] The present invention will be more specifically described
below by way of Examples, but the present invention is not at all
limited to the following exemplifications.
Example 1
(Modification Step)
[0214] 100 parts by mass of a polylactic acid resin ("Biopolymer
Ingeo 4032D" manufactured by Nature Works company, MFR=4.4 g/10
min, density=1240 kg/m.sup.3), and 0.5 part by mass of t-butyl
peroxyisopropyl monocarbonate ("Kayacarbon BIC-75" manufactured by
KAYAKU NOURYON CORPORATION, one-minute half-life temperature T1:
158.8.degree. C.) were stirred and mixed with a ribbon blender to
obtain a mixture.
[0215] The resulting mixture was supplied to a twin screw extruder
(L/D=31.5) having a caliber of 57 mm.
[0216] A preset temperature of a feed part was set at 170.degree.
C., a temperature thereafter was set at 230.degree. C., the
above-mentioned mixture was melted and kneaded in a twin screw
extruder under the conditions of a rotation number of 150 rpm, and
the kneaded product was extruded into a strand shape from a die,
with a caliber of 3 mm and the number of holes of 18, attached to a
tip of the extruder, at a discharge amount of 50 kg/h.
[0217] Then, the extruded strand-like kneaded product was cooled by
being passed through a 2 m length cooling water bath containing
water at 30.degree. C.
[0218] By cutting the resulting strand, modified polylactic acid
resin (mPLA) pellets having the melt tension at 190.degree. C. of
16 cN were prepared.
(Extrusion Step)
[0219] A resin composition containing the modified polylactic acid
resin pellets (mPLA) obtained in the modification step, a crystal
nucleating agent (talc: "CROWN TALC" manufactured by Matsumura
Sangyo Co., Ltd.), and a crystallization accelerator (polyglycerin
fatty acid ester (PGFE): "Tirabazole P4" manufactured by Taiyo
Kagaku Co., Ltd.) at a mass ratio of 100:1:1 (mPLA:talc:PGFE) was
supplied to an extruder, and kneading was performed in the extruder
while heating and melting.
[0220] Thereafter, butane (isobutane/normal butane=70/30) as a
blowing agent was pressed into the same extruder, and melted and
mixed with the above-mentioned resin composition.
[0221] Then, this melt mixture was extrusion expanded from a
circular die to obtain a cylindrical expanded article.
[0222] The resulting cylindrical expanded article was disposed
along an outer peripheral surface of a cooling mandrel, the air was
blown to an outer surface thereof with an air ring larger than a
diameter thereof, and thereby, the article was cooled and formed,
and incised with a cutter at one point on the circumference, to
obtain a belt-like expanded sheet.
[0223] The resulting expanded sheet had an open cell ratio of 21%
and a crystallization degree of 17%.
(Preparation of Resin Molded Article)
[0224] A plug assist-type molding machine including male and female
gratin container-shaped (container opening (including rib) external
dimension: 140 mm, bottom external dimension: 110 mm, container
depth external dimension: 35 mm) forming dies was prepared.
[0225] Thermoforming was performed by setting a die temperature at
120.degree. C., setting the expanded sheet obtained above in the
molding machine, and setting a forming cycle at 6.3 seconds, a
preset temperature of a cavity side heater at 290.degree. C., and a
preset temperature of a plug side heater at 250.degree. C., to
prepare a container (resin molded article).
(Initial Appearance/Crystallization Degree of Resin Molded
Article)
[0226] The container obtained by thermoforming reflected a shape of
the forming die at good precision.
[0227] When a crystallization degree of the container was measured,
a crystallization degree was found to be 37%.
(Initial Appearance/Crystallization Degree/Hot Water Supply
Deformation of Resin Molded Article)
[0228] Boiling water at 100.degree. C. was poured into the
resulting container, hot water was discarded after 3 minutes, and
the swollen situation of the bottom of the container was
observed.
[0229] When the swollen appearance was not seen on the bottom of
the container, or when even if swollen, a height thereof was less
than 3 mm, this was determined that deformation was sufficiently
suppressed, and was determined to be ".circle-w/dot.".
[0230] When a swelling height of the bottom of the container was 3
mm or more and less than 6 mm, this was determined to be an
acceptable range, and was determined to be ".largecircle.".
[0231] On the other hand, when a swelling height of the bottom of
the container was 6 mm or more and less than 9 mm, this was
determined to be "problematic", and determined to be ".DELTA.".
[0232] Further, when the bottom of the container had been swollen 9
mm or more, this was determined that deformation was large, and was
determined to be "x".
[0233] The above assessment results are shown in Table 1.
Example 2, Comparative Examples 1 and 2
[0234] In the same manner as that of Example 1 except that the
contents of the crystal nucleating agent and the crystallization
accelerator were changed, and that the cooling conditions after
extrusion expansion were changed to change a crystallization degree
of the expanded sheet, expanded sheets were prepared and containers
were prepared, and assessment was performed as in Example 1.
[0235] Results are shown in Table 1.
Comparative Example 3
[0236] In the same manner as that of Example 1 except that
unmodified polylactic acid resin pellets were used in the expansion
step, and that the contents of the crystal nucleating agent and the
crystallization accelerator were changed, assessment was
performed.
[0237] However, regarding Comparative Example 3, since the resin
had no melt tension, and stable take-off of the sheet could not be
performed, an expanded sheet was not obtained.
[0238] Results are shown in Table 1.
TABLE-US-00001 TABLE 1 Comparative Comparative Comparative Example
1 Example 2 Example 1 Example 2 Example 3 Physical properties of
modified (unmodified) Unmodified polylactic acid: 100 100 100 100
100 polylactic acid resin 4032D (parts) Amount of organic peroxide
0.5 0.5 0.5 0.5 0 (parts) Melt tension (cN) 16.0 16.0 16.0 16.0 0.9
MFR (g/10 min) 3.0 3.0 3.0 3.0 4.4 Expanded Composition of expanded
sheet Modified polylactic acid resin 100 100 100 100 100 sheet Talc
(parts) 1 1 1 3 1 Crystallization accelerator 1 2 0 0 0 (parts)
Expansion ratio Times 4.7 4.5 6.5 5.0 Unable to Open cell ratio of
expansion sheet % 21 21 15 18 be sheeted Forming cycle [sec] 6.3
6.3 6.3 6.3 Hot water supply Container bottom [mm] 2 4 7.5 11
deformation swelling Assessment .circle-w/dot. .largecircle.
.DELTA. X Crystallization Expanded sheet % 17 16 13 15 degree Resin
molded % 37 36 23 40 article (container)
[0239] As is also apparent from the above-mentioned table,
according to the present invention, there is obtained a resin
molded article that can easily retain a predetermined shape.
* * * * *